Ultrasound presence detectors send out a burst (or continuous) wave of ultrasound and the echoes received at the detector from the environment are used to determine whether an object (e.g. a person) is present in a space (e.g. a room). Different methods can be used for such presence detection, such as Doppler shift measurements, time-of-flight measurements and moving target indicator (MTI) processing. Presence information obtained by presence detectors can be used in a lighting system for controlling one or more lighting devices.
When using presence detectors in a large open space (e.g. an open office), several detectors are needed to cover the space. For reducing the risk of interference between the detectors, time division multiplexing techniques may be used. With time division multiplexing techniques, each detector has a unique time slot, in which the detector performs the presence detection.
Communication infrastructures (or protocols), such as I2C, UART (Universal Asynchronous Receiver/Transmitter), DALI (Digital Addressable Lighting Interface) and ZigBee, may be used in lighting systems for communicating data between different parts of the lighting system.